#include <math.h>
#include <stdlib.h>
#include "tape.h"
#include "record.h"
#include "heap.h"
#include "common.h"

#define SGN(x) ((x > 0) - (x < 0))

char* tmp_format = "tmp.%s.tape";

typedef struct {
    record_t record;
    tape_t*  tape;
} entry_t;

char chartosymbol(unsigned id) {
    // normalize id
    id = id % 62;

    if (id < 26) {
        return 'a' + id;
    } else if (id < 52) {
        return 'A' + id - 26;
    } else if (id < 62) {
        return '0' + id - 52;
    } else {
        return '?';
    }
}

void identifier(unsigned id, char* string) {
    // 26 letters 26 capitals 10 digits
    const unsigned base = 26 + 26 + 10;

    unsigned reminder, i = 0;
    do {
        reminder = id % base;
        string[i++] = chartosymbol(reminder);
    } while (id /= base);
    
    string[i] = 0;
}

tape_t* tape_tmp(unsigned id, const char* mode, const char* format) {
    char tmpname[256], ident[20];

    identifier(id, ident);
    sprintf(tmpname, format, ident);

    return tape_open(tmpname, mode);
}

void help(const char* name)  {
    printf(
        "Sorts reocrds from tape.\n"
        "Usage:\n"
        "\t%s <in-tape> <out-tape>\n",
        name
    );
}

int compare_records(const void* a, const void* b) {
    double result = record_compare(*(record_t*)a, *(record_t*)b);
    return SGN(result);
}

int compare_entries(const void* a, const void* b) {
    const entry_t* lhs = a;
    const entry_t* rhs = b;

    return compare_records(&lhs->record, &rhs->record);
}

void save_sorted(tape_t* tape, record_t* buffer, size_t n) {
    qsort(buffer, n, sizeof(record_t), compare_records);

    for (size_t j = 0; j < n; j++) {
        tape_write(tape, buffer + j, sizeof(record_t));
    }
}

size_t make_series(tape_t* in, size_t n) {
    const size_t max = PAGE_SIZE / sizeof(record_t) * (n + 1);

    size_t series = 0, i = 0;
    record_t* buffer = malloc(PAGE_SIZE * (n + 1));
    
    tape_t* tmp;
    while (tape_read(in, buffer + i++, sizeof(record_t)) > 0) {
        if (i >= max) {
            tmp = tape_tmp(series % n, series >= n ? "ab" : "wb", tmp_format);
            save_sorted(tmp, buffer, i);
            tape_close(tmp);

            i = 0;
            series++;
        }
    }
   
    if (i > 1) {
        tmp = tape_tmp(series % n, series >= n ? "ab" : "wb", tmp_format);
        save_sorted(tmp, buffer, i - 1);
        tape_close(tmp);
        series++;
    }

    free(buffer);
    return series;
}

unsigned join_tapes(tape_t** tapes, size_t n, tape_t* out) {
    heap_t   heap;
    unsigned records = 0;

    heap_init(&heap, n, compare_entries);

    // initial distribution 
    for (unsigned i = 0; i < n; i++) {
        record_t record;

        if (tape_read(tapes[i], &record, sizeof(record_t))) {
            entry_t* entry = malloc(sizeof(entry_t));
            entry->tape    = tapes[i];
            entry->record  = record;

            heap_insert(&heap, entry);
            records++;
        }
    }

    if (!records) {
        return records;
    }

    // merge into 1 tape
    entry_t* current;
    while ((current = heap_pop(&heap))) {
        tape_write(out, &current->record, sizeof(record_t));
        record_t record;
        record_t* result = tape_read(current->tape, &record, sizeof(record_t));

        if (result) {
            if (record_compare(record, current->record) >= 0) {
                current->record = record;
                heap_insert(&heap, current);
                records++;
                continue;
            } else {
                tape_rewind(current->tape, 1, sizeof(record_t));
            }
        }

        free(current);
    }

    heap_free(&heap);

    return records;
}

void print_entry(void* e) 
{
    entry_t* entry = e;
    printf("%lf ", record_length(entry->record));
}

unsigned iteration(size_t i, size_t n)
{
    size_t in_offset  = (i % 2) * n;
    size_t out_offset = ((i+1) % 2) * n;

    unsigned series = 0;

    tape_t** in_tapes  = malloc(n * sizeof(tape_t*));
    tape_t** out_tapes = malloc(n * sizeof(tape_t*));
    heap_t heap;
    heap_init(&heap, n, compare_entries);
    
    for (unsigned i = 0; i < n; i++) {
        in_tapes[i]  = tape_tmp(in_offset + i,  "rb", tmp_format);
        out_tapes[i] = tape_tmp(out_offset + i, "wb", tmp_format);
    }

    while (join_tapes(in_tapes, n, out_tapes[series % n]) > 0) {
        series++;
    }

    for (unsigned i = 0; i < n; i++) {
        tape_close(in_tapes[i]);
        tape_close(out_tapes[i]);
    }

    free(in_tapes);
    free(out_tapes);

    return series;
}

int main(int argc, const char* argv[])
{
    if (argc < 3) {
        help(argv[0]);
        return 0;
    }

    size_t n = 100;

    tape_t* in  = tape_open(argv[1], "rb");
    tape_t* out = tape_open(argv[2], "wb");

    size_t series = make_series(in, n);
    printf("Created %zu series.\n", series);

    unsigned i = 0;
    while (series > n) {
        printf("Iteration %u.\n", i);
        series = iteration(i++, n);
    }

    printf("Final iteration.\n");
    size_t offset = (i % 2) * n;
    tape_t** in_tapes = malloc(series * sizeof(tape_t*));
    for (unsigned i = 0; i < series; i++) {
        in_tapes[i]  = tape_tmp(offset + i,  "rb", tmp_format);
    }

    join_tapes(in_tapes, series, out);

    printf("Sorted file %s into %s in %u iterations.\n", in->name, out->name, i + 1);

    tape_close(in);
    tape_close(out);

    printf("%u IO R: %u W: %u\n", reads + writes, reads, writes);

    return 1;
}