/*
 * postcodeine.c:
 * Given a postcode prefix, plot a map of all the postcodes matching that
 * prefix.
 *
 * Copyright (c) 2006 UK Citizens Online Democracy. All rights reserved.
 * Email: chris@mysociety.org; WWW: http://www.mysociety.org/
 *
 */

static const char rcsid[] = "$Id: postcodeine.c,v 1.5 2006/01/19 19:03:23 chris Exp chris $";

#include <sys/types.h>

#include <ctype.h>
#include <dirent.h>
#include <errno.h>
#include <fcgi_stdio.h>
#include <proj_api.h>
#include <stdbool.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>
#include <unistd.h>

#include <sys/stat.h>

#include "postcodeine.h"

#define MIN_LON         -11.
#define MAX_LON           2.
#define MIN_LAT          49.5
#define MAX_LAT          59.5

#define POSTCODE_CACHE  "/home/chris/projects/postcodeine/data/postcodes.dat"
#define POSTCODE_DIR    "/home/chris/projects/mysociety/codepoint-2005-08/Codepoint_2005.3.0_Aug/sorted"
#define IMAGE_CACHE_DIR "/home/chris/projects/postcodeine/images"

#define die(...)        do { fprintf(stderr, "postcodeine[%d]: ", (int)getpid()); fprintf(stderr, __VA_ARGS__); fprintf(stderr, "\n"); exit(1); } while (0)

struct image images[] = {
        { 301,  400, NULL },
        { 902, 1200, NULL },
    };

#define NIMAGES 2

struct postcodepos {
    char postcode[10];
    double x, y;    /* float'd do */
};

/* clear_image I
 * Clear I. */
static void clear_image(struct image *I) {
    memset((char*)I->data + I->h * sizeof(pixel*), 0, I->h * I->w * sizeof(pixel));
}

/* grid_to_map IRISH E N X Y
 * Convert the grid position (E, N) to an (X, Y) coordinate on the map. If
 * IRISH is true, the Irish grid is used; otherwise OSGB. */
static void grid_to_map(const bool is_irish_grid, const int e, const int n, double *x, double *y) {
    static const char *osgb_params[] = { "+init=world:bng", NULL },
                        /* We have to put this in manually as there is an error
                         * in the file distributed with proj; unfortunately
                         * this does not count as an "important" bug and so
                         * will not be fixed in Debian. */
                      *osni_params[] = { "+proj:tmerc", "+ellps=mod_airy",
                                         "+lat_0=53d30\'N", "+lon_0=8W",
                                         "+x_0=200000", "+y_0=250000",
                                        "k_0=1.000035", "+no_defs", NULL },
                      *merc_params[] = { "+proj=merc", "+ellps=WGS84", NULL };
    static projPJ osgb, osni, merc;
    projUV c1 = {0}, c2 = {0};
    static double E0, N0, E1, N1;
    if (!osgb) {
        /* XXX these seem to abort on failure rather than returning an error */
        if (!(osgb = pj_init(1, (char**)osgb_params)))
            die("%s: pj_init: %s", osgb_params[0], pj_strerrno(pj_errno));
        if (!(osni = pj_init(8, (char**)osni_params)))
            die("%s: pj_init: %s", osni_params[0], pj_strerrno(pj_errno));
        if (!(merc = pj_init(2, (char**)merc_params)))
            die("%s: pj_init: %s %s", merc_params[0], merc_params[1], pj_strerrno(pj_errno));

        /* Figure out bounds of the map. */
        c1.u = MIN_LON * DEG_TO_RAD;
        c1.v = MAX_LAT * DEG_TO_RAD;
        c2 = pj_fwd(c1, merc);
        E0 = c2.u;
        N0 = c2.v;

        c1.u = MAX_LON * DEG_TO_RAD;
        c1.v = MIN_LAT * DEG_TO_RAD;
        c2 = pj_fwd(c1, merc);
        E1 = c2.u;
        N1 = c2.v;
    }

    /* grid to lat/lon. */
    c1.u = e;
    c1.v = n;
    c2 = pj_inv(c1, is_irish_grid ? osni : osgb);

    /* XXX at this point we have a lat/lon registered to the Airy or modified
     * Airy datum. We should transform it to the WGS84 datum using a Helmert
     * transform or whatever, but for this scale it's not really worth the
     * effort. */

    /* lat/lon to Mercator eastings/northings. */
    c1 = pj_fwd(c2, merc);

    *x = (c1.u - E0) / (E1 - E0);
    *y = (c1.v - N0) / (N1 - N0);
}

struct pcindex {
    int first, last;
};

static int tobase36(const char c) {
    if (tolower(c) >= 'a' && tolower(c) <= 'z')
        return tolower(c) - 'a';
    else if (c >= '0' && c <= '9')
        return 26 + c - '0';
    else
        die("bad character '%c'", c);
}

static bool fread_all(void *buf, const size_t n, FILE *fp) {
    return fread(buf, 1, n, fp) == n;
}

static bool fwrite_all(const void *buf, const size_t n, FILE *fp) {
    return fwrite(buf, 1, n, fp) == n;
}

static struct postcodepos *read_postcodes_cached(const char *dir, size_t *npcs, struct pcindex i1[36], struct pcindex i2[36][36], struct pcindex i3[36][36][36]) {
    FILE *fp;
    struct postcodepos *pp;
    int a, b, c;
    struct pcindex ind;

    if (!(fp = fopen(POSTCODE_CACHE, "r")))
        return NULL;

    fprintf(stderr, "postcodeine[%d]: reading cached postcode data\n", (int)getpid());

    if (!fread_all(npcs, sizeof *npcs, fp))
        die("%s: read: %s", POSTCODE_CACHE, strerror(errno));

    pp = malloc(*npcs * sizeof *pp);

    if (!fread_all(pp, *npcs * sizeof *pp, fp))
        die("%s: read: %s", POSTCODE_CACHE, strerror(errno));

    for (a = 0; a < 36; ++a) {
        if (!fread_all(&ind, sizeof(struct pcindex), fp))
            die("%s: read: %s", POSTCODE_CACHE, strerror(errno));
        i1[a] = ind;
        for (b = 0; b < 36; ++b) {
            if (!fread_all(&ind, sizeof(struct pcindex), fp))
                die("%s: read: %s", POSTCODE_CACHE, strerror(errno));
            i2[a][b] = ind;
            for (c = 0; c < 36; ++c) {
                if (!fread_all(&ind, sizeof(struct pcindex), fp))
                    die("%s: read: %s", POSTCODE_CACHE, strerror(errno));
                i3[a][b][c] = ind;
            }
        }
    }

    fclose(fp);

    return pp;
}

/* read_postcodes DIRECTORY
 * Read CSV files containing postcodes and their positions from DIRECTORY. */
static struct postcodepos *read_postcodes(const char *dir, size_t *npcs, struct pcindex i1[36], struct pcindex i2[36][36], struct pcindex i3[36][36][36]) {
    DIR *D;
    struct postcodepos *pp;
    size_t n = 0, nalloc;
    struct dirent *e;
    char fn[256];
    FILE *fp;
    int a, b, c;
    struct pcindex ind;

    if ((pp = read_postcodes_cached(dir, npcs, i1, i2, i3)))
        return pp;
    
    if (!(D = opendir(dir)))
        die("%s: opendir: %s", dir, strerror(errno));
    pp = malloc((nalloc = 100000) * sizeof *pp);
    while ((e = readdir(D))) {
        char *q;
        char line[256];
        int linenum;

        /* Check that the filename ends ".csv" or ".CSV". */
        if ((!(q = strstr(e->d_name, ".csv"))
                    && !(q = strstr(e->d_name, ".CSV")))
            || q[4])
            continue;
        
        sprintf(fn, "%s/%s", dir, e->d_name);
        if (!(fp = fopen(fn, "r")))
            die("%s: open: %s", fn, strerror(errno));

        linenum = 1;
        while (fgets(line, sizeof line, fp)) {
            char *pc, *p;
            int i, j, E, N;

            /* 
             * Example line:
             * "AB119NB",10,"N",18,18,18,0,0,3,0,395004,805097,179,"S00","SN9","00","QA","39","S"
             */

            pc = line + 1;
            p = strchr(pc, '\"');
            if (!p) die("%s:%d: bad data (no quoted postcode)", fn, linenum);
            *(p++) = 0;

            for (i = 0; i < 10; ++i) {
                p = strchr(p, ',');
                if (!p) die("%s:%d: bad data (not enough fields)", fn, linenum);
                ++p;
            }

            if (2 != sscanf(p, "%d,%d,", &E, &N))
                die("%s:%d: bad data (no coordinates)", fn, linenum);

            /* Some postcodes have no valid coordinate data. */
            if (!E && !N)
                continue;

            if (n == nalloc)
                pp = realloc(pp, (nalloc += 1000000) * sizeof *pp);

            for (i = 0, j = 0; pc[i]; ++i)
                if (pc[i] != ' ')
                    pp[n].postcode[j++] = pc[i];
            pp[n].postcode[j] = 0;

            if (pp[n].postcode[strspn(pp[n].postcode, "ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789")])
                die("%s:%d: postcode \"%s\" contains invalid characters", fn, linenum, pp[n].postcode);
            
            grid_to_map(pp[n].postcode[0] == 'B' && pp[n].postcode[1] == 'T', E, N, &pp[n].x, &pp[n].y);

            if (n > 0 && strcmp(pp[n - 1].postcode, pp[n].postcode) >= 0)
                die("%s:%d: postcode \"%s\" does not follow previous postcode \"%s\" lexically", fn, linenum, pp[n].postcode, pp[n - 1].postcode);

            a = tobase36(pp[n].postcode[0]);
            b = tobase36(pp[n].postcode[1]);
            c = tobase36(pp[n].postcode[2]);

            if (i1[a].first == -1) {
                i1[a].first = (int)n;
            }
            i1[a].last = (int)n;
            
            if (i2[a][b].first == -1)
                i2[a][b].first = (int)n;
            i2[a][b].last = (int)n;

            if (i3[a][b][c].first == -1)
                i3[a][b][c].first = (int)n;
            i3[a][b][c].last = (int)n;

            ++linenum;
            ++n;
        }

        if (ferror(fp))
            die("%s: %s", fn, strerror(errno));

        fclose(fp);
    }

    fprintf(stderr, "postcodeine[%d]: writing cached postcode data\n", (int)getpid());
    sprintf(fn, "%s.%d", POSTCODE_CACHE, (int)getpid());
    if (!(fp = fopen(fn, "w")))
        die("%s: open: %s", fn, strerror(errno));

    *npcs = n;
    if (!fwrite_all(npcs, sizeof *npcs, fp)
        || !fwrite_all(pp, n * sizeof *pp, fp))
        die("%s: write: %s", fn, strerror(errno));

    for (a = 0; a < 36; ++a) {
        ind = i1[a];
        if (!fwrite_all(&ind, sizeof(struct pcindex), fp))
            die("%s: write: %s", fn, strerror(errno));
        for (b = 0; b < 36; ++b) {
            ind = i2[a][b];
            if (!fwrite_all(&ind, sizeof(struct pcindex), fp))
                die("%s: write: %s", fn, strerror(errno));
            for (c = 0; c < 36; ++c) {
                ind = i3[a][b][c];
                if (!fwrite_all(&ind, sizeof(struct pcindex), fp))
                    die("%s: write: %s", fn, strerror(errno));
            }
        }
    }

    fclose(fp);

    if (-1 == rename(fn, POSTCODE_CACHE)) {
        unlink(fn);
        die("%s: rename: %s", fn, strerror(errno));
    }

    return pp;
}

static void error(const int code, const char *str) {
    printf(
        "Status: %d %s\r\n"
        "Content-Type: text/plain\r\n"
        "Content-Length: %d\r\n"
        "\r\n"
        "%s\n",
        code, str, strlen(str) + 1, str);
}

int main(int argc, char *argv[]) {
    int i, j, k;
    struct postcodepos *pcs;
    size_t npcs;
    struct pcindex idx1[36], idx2[36][36], idx3[36][36][36];
    extern bool writepng(const char *filename, const struct image *img);
    time_t e;
    struct tm *E;
    char expirydate[32];

    time(&e);
    e += 365 * 86400;
    E = gmtime(&e);
    strftime(expirydate, sizeof expirydate, "%a, %d %b %Y %H:%M:%S GMT", E);

    /* Must do this here so that error-handling works. */
    if (FCGI_Accept() < 0)
        die("first FCGI_Accept() returned < 0");

    fprintf(stderr, "postcodeine[%d]: starting up\n", (int)getpid());
    
    /* Allocate space for the images. */
    for (i = 0; i < NIMAGES; ++i) {
        int y;
        images[i].data = malloc(images[i].h * sizeof(pixel*) + images[i].h * images[i].w * sizeof(pixel));
        for (y = 0; y < images[i].h; ++y)
            images[i].data[y] = (pixel*)((char*)images[i].data + images[i].h * sizeof(pixel*) + y * images[i].w * sizeof(pixel));
    }
    
    /* Initialise the three indices. */
    for (i = 0; i < 36; ++i) {
        idx1[i].first = idx1[i].last = -1;
        for (j = 0; j < 36; ++j) {
            idx2[i][j].first = idx2[i][j].last = -1;
            for (k = 0; k < 36; ++k)
                idx3[i][j][k].first = idx3[i][j][k].last = -1;
        }
    }

    pcs = read_postcodes(POSTCODE_DIR, &npcs, idx1, idx2, idx3);
    
    do {
        char *query;
        int n0, n1;
        struct image *I;
        char fn1[256], fn2[256];
        int c;
        FILE *fp;
        struct stat st;
        float X = 0, Y = 0;

        if (getenv("HTTP_IF_MODIFIED_SINCE")) {
            printf(
                "Status: 304 Not Modified\r\n"
                "Content-Type: image/png\r\n"
                "\r\n");
            continue;
        }

        /* First character is "B" for big map or "S" for small map; remainder
         * is postcode prefix. */
        query = getenv("QUERY_STRING");

        if (!query || !*query || !strchr("BSXZ", *query)) {
            error(400, "Bad query");
            continue;
        }

        if (*query == 'Z') {
            /* List of postcode zones matching. */
            struct postcodezone *Z;
            size_t ql;
            char zone[3] = {0};
            extern struct postcodezone zones[]; /* in zones.c */
            printf(
                "Content-Type: text/html\r\n"       /* sort-of */
                "Expires: %s\r\n"
                "\r\n"
                "<table style=\"width: 100%%;\">"
                "<tr><th style=\"width: 4em;\"></th><th></th></tr>",
                expirydate);
            ql = 0;
            if (query[1] && isalpha(query[1])) {
                zone[0] = query[1];
                ql = 1;
                if (query[2]) {
                    zone[1] = isalpha(query[2]) ? query[2] : 0;
                    ql = 2;
                }
            }
            for (Z = zones; Z->zone; ++Z) {
                if (!query[1] || memcmp(Z->zone, zone, ql) == 0)
                    printf("<tr><td><strong>%.*s</strong>%s</td><td>%s</td></tr>",
                            (int)strlen(zone), Z->zone, Z->zone + strlen(zone), Z->name);
            }
            printf("</table>");
            continue;
        }

        sprintf(fn2, "%s/%s.png", IMAGE_CACHE_DIR, query);
        sprintf(fn1, "%s.%d", fn2, (int)getpid());

        if (*query != 'X' && (fp = fopen(fn2, "r")))
            goto showimage;

        if (*query == 'B')
            I = images + 1;
        else if (*query == 'S')
            I = images;
        else
            I = NULL;
        ++query;
        
        if (query[strspn(query, "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
                                "abcdefghijklmnopqrstuvwxyz"
                                "0123456789")])
            n0 = n1 = -1;
        else if (!*query) {
            n0 = 0;
            n1 = npcs;
        } else {
            int a = -1, b = -1, c = -1;
            a = tobase36(query[0]);
            if (query[1]) {
                b = tobase36(query[1]);
                if (query[2]) c = tobase36(query[2]);
            }

            if (c != -1) {
                size_t l;
                n0 = idx3[a][b][c].first;
                n1 = idx3[a][b][c].last + 1;
                l = strlen(query);

                /* test on I so that the "mean coordinates" mode isn't an
                 * oracle for postcode-to-place lookups. */
                if (l > 3 && I) {
                    /* XXX should bisect */
                    while (strncmp(pcs[n0].postcode, query, l) && n0 < n1) ++n0;
                    if (n0 == n1)
                        n0 = n1 = -1;
                    else {
                        while (strncmp(pcs[n1].postcode, query, l) && n1 > n0) --n1;
                        ++n1;
                    }
                    if (n0 == n1)
                        n0 = n1 = -1;
                }

            } else if (b != -1) {
                n0 = idx2[a][b].first;
                n1 = idx2[a][b].last + 1;
            } else {
                n0 = idx1[a].first;
                n1 = idx1[a].last + 1;
            }
        }

        fprintf(stderr, "query = \"%s\"; from = %d; to = %d\n", query, n0, n1);

        if (I) clear_image(I);
        if (n0 != -1) {
            /* Draw a little square on each bit of the image. */
            int n, d = 1, N;
            if (n1 - n0 > 100000)
                d = 10;
            else if (n1 - n0 > 10000)
                d = 2;
            for (n = n0, N = 0; n < n1; n += d) {
                int x, y, i, j;
                ++N;
                if (!I) {
                    X += pcs[n].x;
                    Y += pcs[n].y;
                    continue;
                }
                x = pcs[n].x * I->w;
                y = pcs[n].y * I->h;
                for (j = y - 1; j <= y + 1; ++j) {
                    if (j < 0 || j >= I->h) continue;
                    for (i = x - 1; i <= x + 1; ++i) {
                        if (i < 0 || i >= I->w) continue;
                        I->data[j][i] = 1;
                    }
                }
            }
            X /= N;
            Y /= N;
        }

        if (!I) {
            char buf[32];
            sprintf(buf, "%.5f,%.5f", X, Y);
            printf(
                "Content-Type: text/plain\r\n"
                "Content-Length: %d\r\n"
                "Expires: %s\r\n"
                "\r\n"
                "%s",
                strlen(buf), expirydate, buf);
            continue;
        }

        /* Write a PNG file. */
        --query;
        writepng(fn1, I);
        rename(fn1, fn2);
     
        if (!(fp = fopen(fn2, "r"))) {
            error(500, strerror(errno));
            continue;
        }

showimage:
        if (-1 == fstat(fileno(fp), &st)) {
            error(500, strerror(errno));
            fclose(fp);
            continue;
        }

        printf(
            "Content-Type: image/png\r\n"
            "Content-Length: %u\r\n"
            "\r\n",
            (unsigned)st.st_size);

        while (EOF != (c = getc(fp)))
            putc(c, stdout);

        fclose(fp);
    } while (FCGI_Accept() >= 0);

    fprintf(stderr, "postcodeine[%d]: shutting down\n", (int)getpid());
    
    return 0;
}