.section .text
.global idt_load
.type idt_load, @function
idt_load:
    mov 4(%esp), %eax
    lidt (%eax)
    ret

/* Common ISR stub */
isr_common_stub:
    pusha

    /* Save segment registers */
    mov %ds, %ax
    push %eax
    
    /* Load kernel data segment */
    mov $0x10, %ax
    mov %ax, %ds
    mov %ax, %es
    mov %ax, %fs
    mov %ax, %gs

    /* Push pointer to stack structure as argument for C handler */
    push %esp
    call isr_handler
    add $4, %esp /* Clean up pushed pointer */

    /* Restore segment registers */
    pop %eax
    mov %eax, %ds
    mov %eax, %es
    mov %eax, %fs
    mov %eax, %gs

    popa
    add $8, %esp /* Cleans up error code and ISR number */
    iret

/* Macro for exceptions with NO Error Code */
.macro ISR_NOERRCODE num
.global isr\num
.type isr\num, @function
isr\num:
    cli
    push $0
    push $\num
    jmp isr_common_stub
.endm

/* Macro for exceptions WITH Error Code */
.macro ISR_ERRCODE num
.global isr\num
.type isr\num, @function
isr\num:
    cli
    push $\num
    jmp isr_common_stub
.endm

ISR_NOERRCODE 0
ISR_NOERRCODE 1
ISR_NOERRCODE 2
ISR_NOERRCODE 3
ISR_NOERRCODE 4
ISR_NOERRCODE 5
ISR_NOERRCODE 6
ISR_NOERRCODE 7
ISR_ERRCODE   8
ISR_NOERRCODE 9
ISR_ERRCODE   10
ISR_ERRCODE   11
ISR_ERRCODE   12
ISR_ERRCODE   13
ISR_ERRCODE   14
ISR_NOERRCODE 15
ISR_NOERRCODE 16
ISR_ERRCODE   17
ISR_NOERRCODE 18
ISR_NOERRCODE 19
ISR_NOERRCODE 20
ISR_NOERRCODE 21
ISR_NOERRCODE 22
ISR_NOERRCODE 23
ISR_NOERRCODE 24
ISR_NOERRCODE 25
ISR_NOERRCODE 26
ISR_NOERRCODE 27
ISR_NOERRCODE 28
ISR_NOERRCODE 29
ISR_ERRCODE   30
ISR_NOERRCODE 31
/* Macro for IRQs (Hardware Interrupts) */
.macro ISR_IRQ num, idt_index
.global irq\num
.type irq\num, @function
irq\num:
    cli
    push $0
    push $\idt_index
    jmp isr_common_stub
.endm

/* Hardware Interrupts */
ISR_IRQ 0,  32
ISR_IRQ 1,  33
ISR_IRQ 2,  34
ISR_IRQ 3,  35
ISR_IRQ 4,  36
ISR_IRQ 5,  37
ISR_IRQ 6,  38
ISR_IRQ 7,  39
ISR_IRQ 8,  40
ISR_IRQ 9,  41
ISR_IRQ 10, 42
ISR_IRQ 11, 43
ISR_IRQ 12, 44
ISR_IRQ 13, 45
ISR_IRQ 14, 46
ISR_IRQ 15, 47

/*
 * INT 0x80 - System call entry point.
 * Uses the same isr_common_stub so the register layout matches registers_t.
 */
.global isr128
.type isr128, @function
isr128:
    cli
    push $0          /* Fake error code */
    push $0x80       /* Interrupt number 128 */
    jmp isr_common_stub

/*
 * tss_flush - Load the Task Register with the TSS selector.
 * TSS is GDT entry 5, selector = 5*8 = 0x28. With RPL=0: 0x28.
 */
.global tss_flush
.type tss_flush, @function
tss_flush:
    mov $0x28, %ax
    ltr %ax
    ret

/*
 * enter_usermode - Switch to Ring 3 user mode via iret.
 * void enter_usermode(uint32_t eip, uint32_t esp);
 *
 * Builds an iret frame on the stack:
 *   SS      = 0x23 (user data)
 *   ESP     = user stack pointer
 *   EFLAGS  = IF=1
 *   CS      = 0x1B (user code)
 *   EIP     = user entry point
 */
.global enter_usermode
.type enter_usermode, @function
enter_usermode:
    mov 4(%esp), %ecx    /* user EIP */
    mov 8(%esp), %edx    /* user ESP */

    /* Set data segment registers to user data segment */
    mov $0x23, %ax
    mov %ax, %ds
    mov %ax, %es
    mov %ax, %fs
    mov %ax, %gs

    /* Build iret frame */
    push $0x23           /* SS (user data) */
    push %edx            /* ESP (user stack) */
    pushf                /* EFLAGS */
    orl $0x200, (%esp)   /* Ensure IF (Interrupt Flag) is set */
    push $0x1B           /* CS (user code) */
    push %ecx            /* EIP (entry point) */
    iret

/*
 * process_switch_to_user - Restore full register state and iret to user mode.
 * void process_switch_to_user(registers_t *regs);
 *
 * Used by process_exit to context-switch to the next process when the normal
 * interrupt-return path isn't available (because we're not returning through
 * an ISR stub). Loads all registers from the registers_t struct and performs
 * iret to enter user mode.
 */
.global process_switch_to_user
.type process_switch_to_user, @function
process_switch_to_user:
    movl 4(%esp), %esp   /* Point ESP to the registers_t struct */

    /* Restore segment register (ds → all data segments) */
    pop %eax
    mov %ax, %ds
    mov %ax, %es
    mov %ax, %fs
    mov %ax, %gs

    popa                  /* Restore EAX-EDI */
    addl $8, %esp         /* Skip int_no and err_code */
    iret                  /* Pops EIP, CS, EFLAGS, UserESP, SS */