// Build a port-compatible RAM dump that has the FS2.1 polygon
// region (file offset $D000+) placed at the dispatcher-expected dest
// address ($BD28 in chicago city RAM).
//
// Usage: extractCityPolygons <city ram dump> <FS2.1 file> <out ram dump>
//
// The chunk5 standard scenery loader (FetchSectorFromDisk →
// ReadBlocks) can't reach FS2.1 blocks past index ~$5F, so the
// polygon region at file offset $D000+ never makes it into RAM via
// fs2trace's normal boot. We manually copy that region into the dump
// at $BD28 (overlaying the database-only section that chunk5 loaded).

#include <stdio.h>
#include <stdint.h>
#include <stdlib.h>
#include <string.h>


int main(int argc, char **argv) {
        if (argc != 4) {
                fprintf(stderr, "usage: %s <city ram dump> <FS2.1 file> <out ram dump>\n", argv[0]);
                return 1;
        }

        FILE *fr = fopen(argv[1], "rb");
        if (fr == NULL) { perror(argv[1]); return 1; }
        uint8_t ram[65536];
        if (fread(ram, 1, 65536, fr) != 65536) {
                fprintf(stderr, "%s: not 64K\n", argv[1]);
                fclose(fr);
                return 1;
        }
        fclose(fr);

        FILE *fp = fopen(argv[2], "rb");
        if (fp == NULL) { perror(argv[2]); return 1; }
        fseek(fp, 0, SEEK_END);
        long pSize = ftell(fp);
        fseek(fp, 0, SEEK_SET);
        uint8_t *poly = malloc(pSize);
        fread(poly, 1, pSize, fp);
        fclose(fp);

        // Polygon region in FS2.1: file offset $D000 onwards (~block
        // 104+). Copy it on top of the city dump's $BD28 so the
        // dispatcher's HEADER target now points to actual polygons
        // instead of the COM/NAV database.
        uint16_t dest = 0xBD28;
        long polyOff = 0xD000;
        long maxLen  = 0xC000 - dest;       // don't cross into $C000 I/O region
        long avail   = pSize - polyOff;
        long copyLen = (avail < maxLen) ? avail : maxLen;
        if (copyLen <= 0) {
                fprintf(stderr, "polygon region empty\n");
                free(poly);
                return 1;
        }
        memcpy(&ram[dest], &poly[polyOff], copyLen);

        FILE *fo = fopen(argv[3], "wb");
        if (fo == NULL) { perror(argv[3]); free(poly); return 1; }
        fwrite(ram, 1, 65536, fo);
        fclose(fo);
        free(poly);
        fprintf(stderr, "Copied %ld bytes from %s @ $%lX to %s @ $%04X\n",
                copyLen, argv[2], polyOff, argv[3], dest);
        return 0;
}